This invention relates to a charged particle beam apparatus, such as an electron beam exposure apparatus, used for drawing or transcribing a pattern on a substrate, and more particularly to a charged particle beam apparatus capable of reducing the amount of carbon compounds and a gas supply/exhaustion method employed therein.
In accordance with the development of integration of LSI devices, there are now strict demands for lithography apparatuses to have a higher precision and throughput. At the present stage, electron beam exposure apparatuses used as lithography apparatuses include drawing apparatuses using reticles (masks) and apparatuses for directly drawing patterns on wafers. To secure a sufficient throughput, these apparatuses employ a variable shaped beam (VSB) method or a character projection (CP) method as an exposure method.
When a pattern is drawn by such an electron beam exposure apparatus, beam drift is exemplified as a cause of degrading the drawing precision. How the drawing precision is degraded by the beam drift will be described using a shaping deflector as an example.
As shown FIG. 2, the shaping deflector is arranged between a first shaping aperture and a second shaping aperture. A deflector plate incorporated in the shaping deflector is made of, for example, Au, Pt, or Al coated with an Au thin film. These materials are used because it is important to keep the deflector plate surface stable. The shaping deflector controls a beam so that an image having passed through the first shaping aperture can be projected onto a predetermined portion of the second shaping aperture. The cause of occurrence of beam drift in the shaping deflector lies in the fact that the image having passed through the first shaping aperture will not be able to be projected onto the predetermined portion of the second shaping aperture with the lapse of time. The beam drift which occurs in the shaping deflector will be referred to as "shaping beam drift".
When shaping beam drift has occurred, the shape and size of the shaping beam will vary with the lapse of time. Accordingly, a shaping beam image of a desired shape and size will not be able to be obtained with the lapse of time, thereby degrading the precision of a drawn pattern.
Moreover, such beam drift may also occur in a deflector for positioning a beam on a desired portion of a sample.
The beam drift is mainly caused by an increase in the charge of substances which is accumulated on deflector electrodes incorporated in the deflector, or on components contained in a beam column near the deflector electrodes. Where non-conductive substances exist near the beam path, they are charged up when radiated with a beam, thereby changing the path of the beam. These non-conductive substances whose charge will increase due to the beam radiation are mainly carbon compounds.
Accumulation of the carbon compounds will appear when residual gases of carbon compounds adsorbed on surface portions of components in the beam column are excited and decomposed by low energy electrons such as secondary electrons.
Part of the residual gases of the carbon compounds consists of a gas which remains in the beam column even after exhaustion of the barrel. Further, a greater part of the residual gases consists of the gas of a carbon compound (mainly as the material of a solvent of a resist) which evaporates from the resist during exposure. This gas is generated whenever the exposure is performed. Accordingly, a great amount of carbon compounds is accumulated upon the components such as the deflector electrodes of the deflector contained in the beam column, thereby causing beam drift and hence serious degradation of drawing accuracy.